/*

 * Licensed to the Apache Software Foundation (ASF) under one

 * or more contributor license agreements.  See the NOTICE file

 * distributed with this work for additional information

 * regarding copyright ownership.  The ASF licenses this file

 * to you under the Apache License, Version 2.0 (the

 * "License"); you may not use this file except in compliance

 * with the License.  You may obtain a copy of the License at

 *

 *     http://www.apache.org/licenses/LICENSE-2.0

 *

 * Unless required by applicable law or agreed to in writing, software

 * distributed under the License is distributed on an "AS IS" BASIS,

 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

 * See the License for the specific language governing permissions and

 * limitations under the License.

 */

package com.bff.gaia.unified.sdk.io.gcp.spanner;



import com.google.auto.value.AutoValue;

import com.google.cloud.spanner.BatchReadOnlyTransaction;

import com.google.cloud.spanner.ResultSet;

import com.google.cloud.spanner.Struct;

import com.google.cloud.spanner.TimestampBound;

import com.bff.gaia.unified.sdk.Pipeline;

import com.bff.gaia.unified.sdk.transforms.DoFn;

import com.bff.gaia.unified.sdk.transforms.PTransform;

import com.bff.gaia.unified.sdk.transforms.ParDo;

import com.bff.gaia.unified.sdk.values.PCollection;

import com.bff.gaia.unified.sdk.values.PCollectionView;

import com.bff.gaia.unified.vendor.guava.com.google.common.annotations.VisibleForTesting;



import javax.annotation.Nullable;



/** A naive version of Spanner read that doesn't use the Batch API. */

@VisibleForTesting

@AutoValue

abstract class NaiveSpannerRead

    extends PTransform<PCollection<ReadOperation>, PCollection<Struct>> {



  public static NaiveSpannerRead create(

      SpannerConfig spannerConfig,

      PCollectionView<Transaction> txView,

      TimestampBound timestampBound) {

    return new AutoValue_NaiveSpannerRead(spannerConfig, txView, timestampBound);

  }



  abstract SpannerConfig getSpannerConfig();



  @Nullable

  abstract PCollectionView<Transaction> getTxView();



  abstract TimestampBound getTimestampBound();



  @Override

  public PCollection<Struct> expand(PCollection<ReadOperation> input) {

    PCollectionView<Transaction> txView = getTxView();

    if (txView == null) {

      Pipeline begin = input.getPipeline();

      SpannerIO.CreateTransaction createTx =

          SpannerIO.createTransaction()

              .withSpannerConfig(getSpannerConfig())

              .withTimestampBound(getTimestampBound());

      txView = begin.apply(createTx);

    }



    return input.apply(

        "Naive read from Cloud Spanner",

        ParDo.of(new NaiveSpannerReadFn(getSpannerConfig(), txView)).withSideInputs(txView));

  }



  private static class NaiveSpannerReadFn extends DoFn<ReadOperation, Struct> {



    private final SpannerConfig config;

    @Nullable private final PCollectionView<Transaction> txView;

    private transient SpannerAccessor spannerAccessor;



    NaiveSpannerReadFn(SpannerConfig config, @Nullable PCollectionView<Transaction> transaction) {

      this.config = config;

      this.txView = transaction;

    }



    @Setup

    public void setup() throws Exception {

      spannerAccessor = config.connectToSpanner();

    }



    @Teardown

    public void teardown() throws Exception {

      spannerAccessor.close();

    }



    @ProcessElement

    public void processElement(ProcessContext c) throws Exception {

      Transaction tx = c.sideInput(txView);

      ReadOperation op = c.element();

      BatchReadOnlyTransaction context =

          spannerAccessor.getBatchClient().batchReadOnlyTransaction(tx.transactionId());

      try (ResultSet resultSet = execute(op, context)) {

        while (resultSet.next()) {

          c.output(resultSet.getCurrentRowAsStruct());

        }

      }

    }



    private ResultSet execute(ReadOperation op, BatchReadOnlyTransaction readOnlyTransaction) {

      if (op.getQuery() != null) {

        return readOnlyTransaction.executeQuery(op.getQuery());

      }

      if (op.getIndex() != null) {

        return readOnlyTransaction.readUsingIndex(

            op.getTable(), op.getIndex(), op.getKeySet(), op.getColumns());

      }

      return readOnlyTransaction.read(op.getTable(), op.getKeySet(), op.getColumns());

    }

  }

}